diff -r 483b0bb23085 -r bde94bd8e8a2 mercurial/interfaces/misc.py
--- a/mercurial/interfaces/misc.py	Sat Feb 08 18:12:29 2025 +0100
+++ b/mercurial/interfaces/misc.py	Sat Feb 08 18:15:18 2025 +0100
@@ -7,6 +7,7 @@
 
 from typing import (
     Callable,
+    Iterator,
     List,
     Protocol,
 )
@@ -24,3 +25,23 @@
     @abc.abstractmethod
     def __call__(self, *args) -> List:
         ...
+
+
+class IDirs(Protocol):
+    '''a multiset of directory names from a set of file paths'''
+
+    @abc.abstractmethod
+    def addpath(self, path: bytes) -> None:
+        ...
+
+    @abc.abstractmethod
+    def delpath(self, path: bytes) -> None:
+        ...
+
+    @abc.abstractmethod
+    def __iter__(self) -> Iterator[bytes]:
+        ...
+
+    @abc.abstractmethod
+    def __contains__(self, d: bytes) -> bool:
+        ...